1. Field of the Invention
This invention relates generally to an electrical switch, and more specifically, this invention relates to an electrical switch in which snap action of movable contacts is achieved in conjunction with a positive override to insure contact breaking in one direction of actuation and a supplemental force to assist in contact breaking in the other direction.
2. Description of the Prior Art
In cam actuated switches, such as those utilized in connection with machine tool controls, it is desirable to cause very rapid opening of the switch contacts, such as by utilization of an overcenter arrangement to achieve snap action. In addition, it is desirable to insure that contact opening will occur even if the overcenter arrangement does not succeed in producing the snap action of the switch contact (e.g., contact welding may occur that the overcenter arrangement is not sufficiently strong to break). This override or assured contact breaking is frequently referred to as a positive break action. Further, it is desirable to assist the return action of the contacts in the event that the overcenter arrangement is not sufficiently strong to produce contact breaking in the direction of actuation.
In addition to providing the positive break snap action in one direction of switch actuation and the supplemental breaking force in the other direction, it is necessary to take into account the fact that in many environments, such as machine tool controls, there are considerable vibrations and other undesired forces acting upon the switch actuating plunger. Accordingly, it is necessary that the switch have a certain amount of free play to prevent undesired switch actuations. At the same time, however, it is necessary that when switch actuation is called for it be done with a snap action to preclude "teasing" or partial openings and closings of the switch contacts. Such teasing or partial makes and breaks of the contacts can result in deleterious arcing producing pitting and other undesired effects of wear of the contacts.
Various types of snap switches have been utilized in the prior art to achieve the desired switch operation. However, none of the prior art switches have been able to successfully combine the features referred to above. Further, many of these prior art approaches have involved relatively expensive switch components and have lacked the desired strength and durability for the type of environment in which such a switch is utilized.